Storage battery electrolyte

ABSTRACT

An improved electrolyte phase for use in high temperature primary and secondary batteries of the thermally or electrically regenerative type. The improved electrolyte phase is made up of a support matrix, which is solid or paste-like at the operating conditions for the battery, and the electrolyte for the battery immobilized and incorporated in the support matrix. The support matrix is made up of an inert alkali metal salt such as alkali metal aluminate. The electrolyte may be an alkali metal halide or mixtures of alkali metal halides.

STORAGE BATTERY ELECTROLYTE BACKGROUND OF THE INVENTION This invention relates to high temperature primary and secondary batteries of either the thermally or electrically regenerative type. More particularly, this invention is directed to a battery electrolyte for use in such batteries.

There exists a class of high temperature electro-chemical and pseudo-electrochemical systems which are used in either electrically or thermally regenerable batteries. When the term high temperature is used herein, it is meant a temperature above the highest of the melting points of the electrolyte and the reactive portions of the electrodes. The high temperatures at which such batteries operate are typically 250300 C. or higher. A typical example of such a pure electrochemical cell (hereinafter referred to as Type I) is a lithium-chlorine battery. In such a battery, the anode is metallic lithium, which is in liquid form at the operating conditions of the battery, and the cathode is a porous carbon electrode with fluid (gaseous) chlorine as the oxidant in association therewith. In such a battery, the anode reaction is:

Li Li e and the corresponding cathode reaction is:

e l/2Cl Cl These reactions produce the overall reaction of:

Li+l/2Cl2- LiCl 3 In such Type I batteries, the electrolytes are typically an alkali metal halide such as lithium chloride, or lithium chloride-lithium fluoride mixture, etc. It will be noted that the electrolyte is preferably a halide salt, or a mixture thereof, of the anode metal. This is also true of the pseudo-electrochemical cells to be described below.

The second type of batteries involved herein, the pseudoelectrochemical cells (hereinafter referred to as Type II), are those having liquid metal cathodes. For example, such a battery may have an alkali metal anode, an alkali metal halide or mixtures of alkali metal halides as the electrolyte, and a cathode formed of relatively low melting point but high boiling point metallic elements or compounds, such as tin. Examples of suitable materials for the anode include lithium, sodium and potassium. Examples of the electrolytes which may be used in such a battery include lithium bromide-lithium fluoride-lithium iodide or lithium fluoride-lithium chloridelithium iodide or other combinations of these salts. Examples of the cathode include tin, antimony, lead, phosphorus, tellurium, selenium, and mixtures or alloys thereof. The electrode and overall cell reactions for a typical example of such a battery are as follows:

Anode: Li Li +3' Cathode: 3 Li Sn LiSn (5) Overall: Li+ Sn LiSn (6) Strictly speaking, the Type II cell involves electrochemical reactions in an unusual sense. The anodic reactant, lithium or other alkali metal, and the cathodic reactant, tin or other low melting metal or compound do not react to form an electrochemical compound. Rather, a type of intermetallic compound is formed, and is represented in the above example as LiSn, although the actual intermetallic compound composition may be complex or in other than simple l:l relationship.

The high temperature battery systems described above possess the advantage that the electrodes or the reactants" are maintained in a liquid or fluid condition at the operating temperature of the batteries. When the metallic electrodes are in a liquid condition, they are good conductors and highly reactive, which minimize "polarization" losses, and the cells are highly reversible. Moreover, they can be recharged either by simple electrical recharging in the usual manner by applying reverse voltage or current or they may be thermally regenerated."The thermal regeneration involves a process in which the metal-metal compound formed in discharge of the battery, the LiSn in the above example, is separated into two metals, one liquid in form and the other vaporous, by a near isothermal distillation-like process at or above the boiling temperature of the anode material. In the case oflithium-tin cells, lithium can be removed from the lithium-tin intermetallic compound by distilling the small amount oflithium away from the excess tin. The vaporous lithium may then be condensed and returned to the anode chamber as a liquid at the ambient temperature of the cell while the liquid tin is returned to the base of the cathode chamber by convection or pumps. In the cathode chamber, the intermetallic compound is formed again by the operation of the battery on discharge, and passes again into a distillation chamber for the regeneration."

Both of the above-described types of high temperature cells are known and have been operated experimentally under laboratory conditions. However, there are serious problems encountered in the practical utilization of such batteries, particularly if such batteries are to be stacked into multiple cell batteries. One of the major problems with these cells is that at the operational temperature, the electrodes, as well as the electrolytes, are at a fluid condition. As indicated above, the liquid condition of the components of the cell contributes to the very low polarization losses of such cells. However, these fluid components or phases in a cell must be kept separate since, for example, a liquid lithium anode may react explosively with the cathode material if direct contact between the two components is permitted to take place. In the laboratory, such fluid phases in the cell are maintained separate by the density differences between the phases. As an example, in the lithiumtin cell described above, the tine cathode is the densest phase and it forms the bottom layer in the cell, the intermediate density electrolyte forms the middle layer in the cell, while the lightest lithium anode phase floats on top of the electrolyte layer. However, since there is a net transfer of matter from the anode to the cathode, the phases must be free to move. Moreover, there must be good contact between the phases for the operation of the battery. During the course of the reaction, there is a decreasing volume of material at the anode and an increasing volume at the cathode. The mass transfer and the change in volume tends to disturb the interfaces. Of course, it is clear that the maintaining of separate fluid phases in such batteries by density gradients is not feasible if the battery is used in a moving vehicle or non-gravational field. Finally, it is not feasible to stack a plurality of such cells while maintaining three distinct liquid phases in each cell, to form a multiple-cell battery system.

It is, therefore, an object of the invention to provide an improved high temperature battery which contains an improved electrolyte capable of separating the fluid electrodes.

It is another object of the invention to provide an improved high temperature battery having fluid electrodes which may be used in a moving and non-gravitational vehicle.

It is a further object ofthe invention to provide an improved high temperature battery which has a stable electrolyte composition resistant to attacks by the corrosive components in I such battery.

It is still another object of the invention to provide an improved high temperature battery which can be stacked to form a multicell battery system.

Still further objects of the invention can be gathered from the following description.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a high temperature battery having fluid electrodes, wherein the electrolyte phase is made of a solid or paste-like support matrix made from an inert alkali metal salt and having the electrolyte for said battery incorporated and immobilized therewithin. The support matrix for the electrolyte phase of the battery is prepared from a truly inert alkali metal salt so that it is resistant to corrosion or attack by the highly reactive components within the battery. The support matrix should also have a solid or a paste-like consistency and rheology at United States Patent Baker 1 May 16, 1972 [54] STORAGE BATTERY ELECTROLYTE 3,510,359 5/1970 Selover et a1. ..136/1 53 [72] Inventor: Bernard S. Baker, Chicago, lll. FOREIGN PATENTS OR APPLICATIONS 1 1 Assisneel Institute of Gas Technology 1,502,386 11/1967 France ..136/153 22 F'] d: M 14 19 9 l l e ay 6 Primary Examiner-Donald L. Walton [21] Appl. No.: 824,707 Att0rneyBair, Freeman & Molinare 57 ABSTRACT [52] U.S. Cl ..136/6, 136/153 1 [5]] An improved electrolyte phase for use in high temperature 58 Field of Search ..136/6, 86, 153, 146,83 p y and secondary batteries of the thermally or e18mically regenerative type. The improved electrolyte phase is 56] References Cited made up of a support matrix, which is solid or paste-like at the operating conditions for the battery, and the electrolyte for UNITED STATES PATENTS the battery immobilized and incorporated in the support matrix. The support matrix is made up of an inert alkali metal 3,257,239 6/1966 ShilltZ et al. 1 36/86 Salt Such as alkali metal aluminate The electrolyte y be an 31488221 H1970 Shlmotake et 1 36/6 X alkali metal halide or mixtures of alkali metal halides. 2,276,188 10/1939 Greger ..136/153 3,419,436 12/1968 Recht et a] ..136/153 9 Claims, No Drawings EXAMPLE 5 The procedure of Example 2 was repeated except that 50 percent lithium aluminate was mixed with 50 percent of an alkali metal halide mixture. A pellet 0.238 cm thick and 2.86 square cm in area was prepared at a pressure of 8,000 p.s.i. and a temperature of 220 C. The disc was then used in a lithium-tin bimetallic cell operated at 400 C. The disc which represents the electrolyte phase served to effectively separate the two liquid phases of lithium and tin. The separated cell, which has an active area equal to that of the disc (2.86 sq. cm. has a resistance of 0.63 ohm. Table I below shows the instantaneous voltage-current characteristics for dischargecharge conditions for this cell, while Table II shows the voltage-time characteristics of the cell.

Voltage-Time Characteristics of Battery of Example 5 Time (minutes) Voltage (volts) 70 mA rate 170 mA rate The above examples are for illustrative purposes only and that other forms of matrices could be prepared. For example, for high rate short life primary battery applications, very thin matrices might be prepared by flame spraying lithium aluminate on a suitable substrate and then immersing the lithium aluminate structure in the electrolyte to render it conductive. Moreover, the particular pressure and temperature employed in the making of the electrolyte phase pellets given above are only illustrative and other pressures and temperatures may be used therefor.

As noted above, an amount of the lithium aluminate is added to the electrolyte salt to comprise 40 to 65 percent by weight of the total. The electrolyte and aluminate mixture which is solid and in powdered form, is then compressed by standard techniques into a form for use as the electrolyte phase in a high temperature battery. In another embodiment of the invention, the powdered mixture of aluminate and the electrolyte may be used as such, without hot pressing in primary batteries, such as missile batteries, or as the electrolyte sandwich in secondary batteries, such as an automobile battery.

Since the electrolyte salts, i.e., the alkali metal halide mixtures, are the conductive portion of the electrolyte phase of the invention, it is clear that higher conductivities for the electrolyte phase are obtained with a lower percentage of the inert support material. In accordance with the present invention, as

little as about 40 percent of the inert aluminate will form an excellent support for the electrolyte to yield high conductivities.

The invention has been described in detail with reference to particular and preferred embodiments thereof, but it will be understood that variations and modifications can be made within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What is claimed is:

1. In a high temperature storage battery having an anode, cathode, and an electrolyte phase disposed between said anode and said cathode, the improvement wherein:

said cathode is selected from tin, antimony, lead,

phosphorous, sulfur, tellurium, selenium or mixtures or alloy mixtures thereof, and

said electrolyte phase comprises an alkali metal salt electrolyte supported in paste condition at the operating conditions of said battery by a substantially pure and inert alkali metal aluminate matrix in an amount from about 30 to about 60 percent by weight of said electrolyte phase.

2. Battery of claim 1 wherein said inert alkali metal aluminate is prepared from the reaction of a reactive transition alumina with an alkali metal salt.

3. Battery of claim 2 wherein said inert alkali metal aluminate is lithium aluminate prepared from the reaction of lithium carbonate and y-alumina.

4. Battery of claim 2 wherein said inert alkali metal aluminate is sodium aluminate prepared from the reaction of sodium carbonate and y-alumina.

5. Battery of claim 2 wherein said inert alkali metal aluminate is potassium aluminate prepared from the reaction of potassium carbonate and y-alumina.

6. In a high temperature storage battery having an anode, a cathode, and an electrolyte phase disposed between said anode and said cathode, the improvement wherein said anode is an alkali metal, said electrolyte phase comprises an alkali metal salt electrolyte supported by a substantially pure and inert alkali metal aluminate matrix in an amount from about 30 to about 60 percent by weight of said electrolyte phase, and said alkali metal aluminate contains the same alkali metal as said anode.

7. Battery of claim 6 wherein said anode is lithium and said inert alkali metal aluminate is lithium aluminate.

8. Battery of claim 6 wherein said anode is lithium, said cathode is tin, and said electrolyte phase is made of a matrix support formed of lithium aluminate and an electrolyte formed of a mixture of lithium halides.

9. Battery as in claim 6 wherein said cathode is selected from tin, antimony, lead, phosphorous, sulfur, tellurium, selenium or mixtures or alloy mixtures thereof. 

2. Battery of claim 1 wherein said inert alkali metal aluminate is prepared from the reaction of a reactive transition alumina with an alkali metal salt.
 3. Battery of claim 2 wherein said inert alkali metal aluminate is lithium aluminate prepared from the reaction of lithium carbonate and gamma -alumina.
 4. Battery of claim 2 wherein said inert alkali metal aluminate is sodium aluminate prepared from the reaction of sodium carbonate and gamma -alumina.
 5. Battery of claim 2 wherein said inert alkali metal aluminate is potassium aluminate prepared from the reaction of potassium carbonate and gamma -alumina.
 6. In a high temperature storage battery having an anode, a cathode, and an electrolyte phase disposed between said anode and said cathode, the improvement wherein said anode is an alkali metal, said electrolyte phase comprises an alkali metal salt electrolyte supported by a substantially pure and inert alkali metal aluminate matrix in an amount from about 30 to about 60 percent by weight of said electrolyte phase, and said alkali metal aluminate contains the same alkali metal as said anode.
 7. Battery of claim 6 wherein said anode is lithium and said inert alkali metal aluminate is lithium aluminate.
 8. Battery of claim 6 wherein said anode is lithium, said cathode is tin, and said electrolyte phase is made of a matrix support formed of lithium aluminate and an electrolyte formed of a mixture of lithium halides.
 9. Battery as in claim 6 wherein said cathode is selected from tin, antimony, lead, phosphorous, sulfur, tellurium, selenium or mixtures or alloy mixtures thereof. 